In a wireless network, connectivity and communication between devices is achieved through antennas attached to receivers or transmitters in order to radiate the desired signals to or from other elements of the network. In radio communication systems, such as millimeter-wave radios, discrete components are usually assembled with low integration levels. These systems are often assembled using expensive and bulky waveguides and package-level or board-level microstrip structures to interconnect semiconductors and their required transmitter or receiver antennas.
With recent progress in semiconductor technology and packaging engineering, the dimensions of these radio communication systems have become smaller and integration of antennas with their radio frequency (RF) front-end circuits has become more desirable. For applications such as wireless universal serial bus (USB), the operating distance is limited to about a meter; a single antenna with about 7 dBi at 60 GHz will provide the necessary antenna gains. However, these devices typically operate in indoor environments. As a result, multi-path fading due to multiple reflections and diffractions deteriorates the radio system performance. Numerous studies indicate circularly polarized (CP) antennas can be used to mitigate the multi-path effect on the system performance.
As is well-known to one having skill in the art, packagable CP antennas require three major components: a radiator that can radiate circularly polarized electromagnetic waves (either left- or right-handed), a feeding network for impedance matching and interfacing with semiconductor chips, and a relatively small cavity for use in the packaging process and reducing electromagnetic interference (EMI) to active circuits.
For example, R. Li et al., “Investigation of Circularly Polarized Loop Antennas With a Parasitic Element for Bandwidth Enhancement,” IEEE Transactions on Antennas and Propagation, vol. 54, no. 12, pp. 3930-3939, December 2005, the disclosure of which is incorporated by reference herein, discloses series- and parallel-fed dual rhombic-loop antennas with and without a parasitic dual rhombic loop.